This invention relates to method and apparatus for metering liquid media of different viscosity in offset printing machines. The apparatus preferably serves to meter liquid media for application to a printing carrier in varnishing units. The apparatus is suitable for
processing low-viscosity (.ltoreq.50s outflow time 4 mm Becher) media such as dispersion varnish on an aqueous basis and is also suitable for processing higher-viscosity (&gt;50s outflow time 4 mm Becher) media such as bronze/effect printing ink with a defined pigment proportion (e.g., gold varnish).
Various solutions are known for applying liquid media. According to DE 3 427 898 C1, the feed of the media to be applied takes place by means of a metering roller and an applicator roller by the squeeze roller principle, the liquid (e.g., varnish) being fed to the nip between the rollers by means of a tube via a wedge of varnish.
A chamber-type doctor of the type known from EP 0 071 180 A1 is essentially formed by a housing with side walls and by doctor blades attached to the housing. The doctor blades are supported on a screened applicator roller, and the liquid is transferred onto the applicator roller via the chamber thus formed. In this case, the chamber-type doctor is mounted pivotably in a holder arranged above the applicator roller and can be engaged against the applicator roller by an operating cylinder acting on the holder.
These solutions are disadvantageous in that they do not guarantee precise metering (generating a defined layer thickness) of the media to be applied with media of different viscosity. The known solutions thus cannot be used universally for applying the media used by various printing carriers.
An applicator unit for printing machines is known according to DE 3,906,648 A1 and is suitable for high-viscosity and low-viscosity media. In this case, the metering take place essentially by means of a profiled dip roller, a doctor blade, a transfer roller and smoothing rollers or by means of an applicator roller and a forme cylinder, provided with wells, with a doctor blade.
These designs are complex in construction, in particular when using smoothing rollers.